It is known that lubricating compositions become less effective during their use due to exposure to the operating conditions of the device they are used in, and particularly due to exposure to by-products generated by the operation of the device. For example, engine oil becomes less effective during its use, in part due to exposure of the oil to acidic and pro-oxidant by-products. These by-products result from the incomplete combustion of fuel in devices such as internal combustion engines, which utilize the oil. These by-products lead to deleterious effects in the engine oil and likewise in the engine. The by-products may, for example, oxidize hydrocarbons found in the lubricating oil, yielding carboxylic acids and other oxygenates. These oxidized and acidic hydrocarbons can then go on to cause corrosion, wear and deposit problems.
Base-containing additives are added to lubricating compositions in order to neutralize such by-products, thus reducing the harm they cause to the lubricating composition and to the device. Over-based calcium or magnesium carbonate detergents have been used for some time as acid scavengers, neutralizing these by-products and so protecting both the lubricating composition and the device. However, over-based detergents carry with them an abundance of metal as measured by sulfated ash. Industry upgrades for diesel and passenger car lubricating oils are putting ever decreasing limits on the amount of sulfated ash, and by extension the amount of over-based detergent, permissible in an oil. Therefore, a source of base that consists of only N, C, H, and O atoms is extremely desirable.
There are two common measures of basicity that are used in the field of lubricating composition additives. Total Base Number (TBN) may be as measured by ASTM D2896, which is a titration that measures both strong and weak bases. On the other hand, ASTM D4739 is a titration that measures strong bases but does not readily titrate weak bases such as certain amines, including many aromatic amines. Many lubricating composition applications desire TBN as measured by ASTM D4739, making many amines less than satisfactory sources of basicity. As used herein, TBN (total base number) values are measured by the methodology described in ASTM D2896 unless otherwise specifically noted.
Basic amine additives have nevertheless been investigated as alternatives to ash containing over-based metal detergents, for example, alkyl and aromatic amines. However, the addition of basic amine additives can lead to additional detrimental effects. For example, it is known that alkyl and some aromatic amines tend to degrade fluoroelastomeric seals materials. These basic amine additives, such as succinimide dispersants, contain polyamine groups, which provide a source of basicity. However, such amines are believed to cause dehydrofluorination in fluoroelastomeric seals materials, such as Viton® seals, which is believed to be a first step in seals degradation. Seal degradation may lead to seal failure, such as seal leaks, harming engine performance and possibly causing engine damage. Generally, the base content, or total base number (TBN), of a lubricating composition can only be boosted modestly by such a basic amine before seals degradation becomes a significant issue, limiting the amount of TBN that can be provided by such additives.